1. Anatomy of female genital organs (must know, we will not analyze) 2. Dimensions of the major pelvis (D. spinarum, D. cristarum, D. trochanterica, S. diagonalis, S. externa, S. vera) 3. Dimensions of the minor pelvis (dimensions of 4 planes: entrance, wide, narrow, exit) 4. Dimensions of the fetal head 5. Determination of the gestational age and date of birth 6. Methods of diagnosing pregnant women 7. Method of palpation (Leopold-Levitsky) 8. Auscultation of the fetus 9. estimated fetal weight
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Here is a comprehensive study guide covering all 8 topics (anatomy of female genitalia is excluded per your note):
Obstetrics Study Guide
2. Dimensions of the Major (Greater) Pelvis
The major pelvis is bounded by the iliac wings and does not directly form the birth canal, but its external measurements are used clinically to indirectly estimate the dimensions of the minor pelvis.
The standard external pelvimetry measurements are:
| Measurement | Latin Name | Normal Value | Description |
|---|---|---|---|
| Distantia spinarum | D. spinarum | 25–26 cm | Distance between the two anterior superior iliac spines (ASIS) |
| Distantia cristarum | D. cristarum | 28–29 cm | Greatest distance between the left and right iliac crests |
| Distantia trochanterica | D. trochanterica | 30–31 cm | Distance between the greater trochanters of the femur |
| Conjugata diagonalis | S. diagonalis | 12.5–13 cm | Distance from sacral promontory to the lower border of the pubic symphysis (measured vaginally) |
| Conjugata externa (Baudelocque) | S. externa | 20–21 cm | Distance from the upper border of the symphysis to the spinous process of L5 |
| Conjugata vera (obstetrica) | S. vera | 11 cm | The TRUE obstetric conjugate — smallest AP diameter of the pelvic inlet, from sacral promontory to the posterior border of symphysis |
Clinical formula: S. vera = S. diagonalis − 1.5–2 cm (it cannot be measured directly; it is derived from the diagonal conjugate).
— General Anatomy and Musculoskeletal System (THIEME Atlas), p. 162
3. Dimensions of the Minor (Lesser) Pelvis — 4 Planes
The lesser pelvis forms the actual birth canal. It is described by four planes, each with its own critical measurements.
Plane 1: Pelvic Inlet (Entry/Superior Strait)
The inlet is bounded by the sacral promontory posteriorly, the lineae terminales laterally, and the superior border of the pubic symphysis anteriorly.
| Diameter | Value | Description |
|---|---|---|
| Conjugata vera (AP) | 11 cm | Sacral promontory → posterior symphysis (smallest, most critical) |
| Transverse diameter | 13 cm | Greatest width between lineae terminales |
| Oblique diameters (right & left) | 12 cm | Sacroiliac joint → iliopectineal eminence on opposite side |
Plane 2: Wide Part (Plane of Greatest Dimensions)
Located at the level of the acetabulum and S2–S3.
| Diameter | Value |
|---|---|
| AP diameter | 12.5 cm |
| Transverse diameter | 12.5 cm |
Plane 3: Narrow Part (Plane of Least Dimensions)
The most clinically relevant plane — where arrest of descent most often occurs. Bounded by the ischial spines, tip of the sacrum, and lower symphysis.
| Diameter | Value | Description |
|---|---|---|
| AP diameter | 11.5 cm | Lower symphysis → tip of sacrum |
| Interspinous (transverse) | 10–11 cm | Distance between the ischial spines — the narrowest part of the pelvis |
Plane 4: Pelvic Outlet (Exit/Inferior Strait)
Diamond-shaped. Bounded by the pubic arch, ischial tuberosities, sacrotuberous ligaments, and coccyx.
| Diameter | Value | Description |
|---|---|---|
| AP diameter (anatomic) | 9 cm | Lower symphysis → coccyx tip |
| AP diameter (obstetric) | 11 cm | Lower symphysis → sacrum (coccyx deflects backward during delivery, adding ~2 cm) |
| Transverse (intertuberous) | 10–11 cm | Distance between ischial tuberosities |
The interspinous diameter of the narrow plane (10–11 cm) and the true conjugate of the inlet (11 cm) are the two most important obstetric measurements.
— General Anatomy and Musculoskeletal System (THIEME Atlas), p. 162
4. Dimensions of the Fetal Head
The fetal head is the largest and least compressible presenting part. Its dimensions relative to the pelvis determine whether vaginal delivery is possible.
Key Diameters
| Diameter | Value | Description |
|---|---|---|
| Biparietal diameter (BPD) | 9.5 cm | Between the two parietal eminences (transverse — the widest transverse dimension) |
| Suboccipito-bregmatic | 9.5 cm | From the nape of the neck to the center of the anterior fontanelle; presents in complete flexion (vertex OA) — most favorable |
| Occipito-frontal | 12 cm | From the occiput to the frontal bone; presents in partial deflexion |
| Mento-vertical (trachelobregmatic) | 13.5 cm | Largest — from the chin to the vertex; presents in brow presentation — least favorable |
| Suboccipito-frontal | 10.5 cm | Subocciput to the frontal bone |
| Occipito-mental (mento-occipital) | 13.5 cm | Occiput to chin |
Key Circumferences
| Circumference | Value | Presentation |
|---|---|---|
| Suboccipito-bregmatic | 32 cm | Fully flexed vertex |
| Occipito-frontal | 34 cm | Partially deflexed |
| Occipito-mental | 35–36 cm | Extended (face) |
Transverse Diameters of the Head
| Diameter | Value |
|---|---|
| Biparietal (BPD) | 9.5 cm |
| Bitemporal | 8 cm |
The most favorable presenting diameter is the suboccipito-bregmatic (9.5 cm) — it matches the interspinous diameter of the pelvic narrow plane, allowing passage in complete flexion.
5. Determination of Gestational Age and Expected Date of Birth (EDD)
Gestational Age Calculation Methods
| Method | How It Works |
|---|---|
| Naegele's Rule (LMP) | EDD = LMP + 9 months + 7 days (or LMP − 3 months + 7 days + 1 year) |
| Ultrasound — Crown-Rump Length (CRL) | Most accurate in first trimester (±5–7 days before 14 weeks) |
| Ultrasound — BPD / Head Circumference | Used in 2nd trimester; less accurate (±2 weeks at 20 wks) |
| Ultrasound — BPD + FL + AC combination | Standard 2nd/3rd trimester dating |
| Fundal height (Bartholomew's rule) | Height of uterine fundus in cm ≈ gestational age in weeks after 20 weeks |
| Quickening | Primigravida: ~20 weeks; Multigravida: ~18 weeks |
| Fetal heart tones | Doppler: ~10–12 weeks; Fetoscope (Pinard): ~18–20 weeks |
Bartholomew's Rule of Fundal Height
| Weeks | Fundal Level |
|---|---|
| 12 wks | Just above pubic symphysis |
| 16 wks | Midway between symphysis and umbilicus |
| 20 wks | At the umbilicus |
| 28 wks | 3 finger-widths above umbilicus |
| 36 wks | At the xiphoid/costal margin |
| 40 wks | Drops slightly below xiphoid (lightening) |
Naegele's Rule Example
- LMP: January 1 → EDD: October 8 of same year
6. Methods of Diagnosing Pregnancy
Presumptive (Subjective) Signs
- Amenorrhea
- Nausea/vomiting ("morning sickness"), especially 6–12 weeks
- Breast tenderness, enlargement, darkening of areola
- Fatigue, urinary frequency
- Quickening (fetal movement perception)
- Skin changes: chloasma (melasma), linea nigra
Probable (Objective) Signs
- Hegar's sign: softening of the isthmus of the uterus (6–8 weeks)
- Chadwick's sign: bluish-violet discoloration of vagina and cervix (due to increased vascularity)
- Goodell's sign: softening of the cervix
- Piskacek's sign: asymmetrical enlargement of the uterus near implantation site
- Positive pregnancy test (hCG): urine or serum β-hCG — detectable 8–10 days after fertilization; serum quantitative most sensitive
- Uterine enlargement
- Ballottement of the fetus (16–28 weeks)
Positive (Definitive) Signs
- Fetal heart tones heard on auscultation or Doppler
- Fetal movement felt by examiner
- Ultrasound visualization of the gestational sac (5 weeks), fetal pole + cardiac activity (6–7 weeks)
7. Leopold-Levitsky Maneuvers (Пальпація за Леопольдом-Левіцьким)
The four Leopold maneuvers are systematic abdominal palpations performed after 28 weeks to assess fetal lie, presentation, position, and engagement. The examiner stands facing the patient for maneuvers 1–3, then faces the patient's feet for maneuver 4.
Maneuver I — Fundal Grip
Purpose: Determine what fetal part occupies the fundus.
- Technique: Both hands palpate the fundal area.
- Findings:
- Soft, irregular mass = buttocks → vertex presentation
- Hard, round, ballotable mass = head → breech presentation
Maneuver II — Lateral/Umbilical Grip
Purpose: Determine fetal lie and locate the back.
- Technique: Both hands placed on lateral sides of the abdomen; one hand steady, the other palpates.
- Findings:
- Firm, smooth, continuous resistance = fetal back
- Irregular, knobby resistance = small parts (limbs)
- Also helps determine position (e.g., LOA, ROA)
Maneuver III — Pawlik's Grip (Lower Pole)
Purpose: Determine the presenting part and its mobility.
- Technique: Single hand grasps the lower uterine segment just above the pubic symphysis between thumb and fingers.
- Findings:
- Hard, round, ballotable = head (not yet engaged)
- Soft, irregular = breech
- If immovable → presenting part is engaged
Maneuver IV — Pelvic Grip (Engagement)
Purpose: Confirm presenting part and assess degree of engagement/descent into the pelvis.
- Technique: Examiner faces the feet; both hands placed on either side of the lower uterus, fingers directed toward the pelvic inlet.
- Findings:
- Hands converge easily = head is engaged (below the inlet)
- Hands diverge = head is not engaged (ballotable above inlet)
- The cephalic prominence (brow) identifies flexion vs. deflexion
Fetal heart tones (Maneuver II correlation): best heard through the fetal back — located using Maneuver II. In vertex presentations, FHT heard below the umbilicus; in breech, above the umbilicus.
— Textbook of Family Medicine 9e
8. Auscultation of the Fetal Heart
Equipment
- Pinard fetoscope (wooden/metal horn): audible from ~18–20 weeks
- Doppler ultrasound: audible from ~10–12 weeks
- Cardiotocograph (CTG): continuous monitoring from ~28 weeks
Normal Fetal Heart Rate
- 110–160 beats per minute (bpm)
Auscultation Sites (by fetal position)
| Fetal Position | Best Auscultation Point |
|---|---|
| LOA (Left Occiput Anterior) | Left lower quadrant (most common) |
| ROA (Right Occiput Anterior) | Right lower quadrant |
| LOP (Left Occiput Posterior) | Left flank |
| ROP (Right Occiput Posterior) | Right flank |
| Frank Breech | At or above umbilicus |
| Complete/Footling Breech | At or above umbilicus |
Technique
- Identify the fetal back using Leopold Maneuver II.
- Place the Pinard fetoscope/Doppler over the fetal scapular area (back) in vertex presentations.
- Count beats for 1 full minute (or 15 sec × 4).
- Differentiate FHT from maternal pulse (palpate maternal radial pulse simultaneously).
Interpretation
- Normal: 110–160 bpm, regular
- Tachycardia: >160 bpm (fetal distress, fever, hypoxia, drugs)
- Bradycardia: <110 bpm (cord compression, placental insufficiency)
9. Estimated Fetal Weight (EFW)
Clinical (External) Methods
Johnson's Formula (based on fundal height):
EFW (g) = (Fundal height in cm − 11) × 155
(Subtract 12 instead of 11 if the head is engaged)
Lebedenko/Stroganova Formula:
EFW = abdominal circumference (cm) × fundal height (cm)
(e.g., AC = 90 cm, FH = 32 cm → EFW ≈ 2880 g)
Ultrasound-Based EFW (Hadlock Formula)
Uses combinations of:
- BPD (biparietal diameter)
- HC (head circumference)
- AC (abdominal circumference) — most sensitive single parameter for fetal weight
- FL (femur length)
The most widely used Hadlock formula:
log₁₀(EFW) = 1.3596 + 0.0064(HC) + 0.0424(AC) + 0.174(FL) + 0.00061(BPD × AC)
(EFW in grams; measurements in cm)
Weight Categories at Term
| Category | Weight |
|---|---|
| Low birth weight | < 2500 g |
| Normal term | 2500–4000 g |
| Macrosomia | > 4000 g |
| Large for gestational age (LGA) | > 90th percentile |
— Creasy & Resnik's Maternal-Fetal Medicine; Thompson & Thompson Genetics in Medicine
Quick Reference Summary Card
| Topic | Key Numbers to Memorize |
|---|---|
| D. spinarum | 25–26 cm |
| D. cristarum | 28–29 cm |
| D. trochanterica | 30–31 cm |
| S. diagonalis | 12.5–13 cm |
| S. externa | 20–21 cm |
| S. vera | 11 cm (= diagonalis − 1.5–2 cm) |
| Pelvic inlet: AP / transverse / oblique | 11 / 13 / 12 cm |
| Pelvic narrow plane: AP / interspinous | 11.5 / 10–11 cm |
| Pelvic outlet: AP (obstetric) / transverse | 11 / 10–11 cm |
| Fetal BPD | 9.5 cm |
| Suboccipito-bregmatic | 9.5 cm — MOST FAVORABLE |
| Normal FHR | 110–160 bpm |
| Normal term birth weight | 2500–4000 g |
| Naegele's Rule | LMP + 9 months + 7 days |
Sources used: General Anatomy and Musculoskeletal System (THIEME Atlas), Creasy & Resnik's Maternal-Fetal Medicine, Textbook of Family Medicine 9e, and standard obstetric reference values.
Most critical exam numbers to nail:
- S. vera = 11 cm (derived: diagonalis − 1.5–2 cm)
- Interspinous = 10–11 cm (narrowest point of birth canal)
- Suboccipito-bregmatic head diameter = 9.5 cm (most favorable presentation)
- Normal FHR = 110–160 bpm
- The four Leopold maneuvers: fundal → lateral → lower pole → engagement
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